Mishkat al-Masabih 7 Fasting كتاب الصوم 66

وَعَنْ أَنَسٍ قَالَ: كُنَّا مَعَ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فِي السَّفَرِ فَمِنَّا الصَّائِمُ وَمِنَّا الْمُفْطِرُ فَنَزَلْنَا مَنْزِلًا فِي وم حَارٍّ فَسَقَطَ الصَّوَّامُونَ وَقَامَ الْمُفْطِرُونَ فَضَرَبُوا الْأَبْنِيَةَ وَسَقَوُا الرِّكَابَ. فَقَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «ذَهَبَ الْمُفْطِرُونَ الْيَوْمَ بِالْأَجْرِ»

Anas said that in the course of a journey with the Prophet when some of them were fasting and others broke their fast, they alighted at a stage on a hot day, and while those who fasted collapsed those who had broken their fast rose and set up the tents and watered the riding-beasts, whereupon God’s messenger said, “Those who broke their fast have earned all the reward today.” (Bukhari and Muslim.)